In usual prior art extrusion processes a thermoplastic of a single color is fed to an extrusion head to form a part, which may constitute a parison for use in a subsequent blow molding operation. In certain extrusion processes, plastics of two or more different colors have been simultaneously fed into an extrusion head to form parts with stripes extending in the extrusion direction.
In the normal forming of blow molded products, a parison formed of thermoplastics is extruded and then captured in a mold where it is blown into a shape. This method is used to form containers such as bottles and cups.